Não
tenho tido muito tempo pra escrever no blog do PollingData. Pra compensar, vou
reproduzir parte de um artigo escrito pelo Gelman que foi publicado no
Washington Post sobre pesquisas eleitorais. O começo do artigo discute alguns
detalhes metodológicos sobre pesquisas telefônicas/online feitas nos EUA. Mas o
final vale pra qualquer lugar, qualquer metodologia. Segue um parágrafo que eu
gosto bastante, que resume também minha opiniao sobre a existência de
amostragem probabilística (em inglês):
"In real life there are no probability samples of
humans. With survey response rates below 10 percent, there is no way to know
the probability of an individual being included in the sample. You can know the
probability that the survey organization will try to reach a
person — that’s easy, it just depends on exactly how the address or telephone
number or e-mail is sampled from a given list. But it’s impossible to know the
probability that this person will actually be included in the sample, as this
depends on the probability that the person is reached, multiplied by the probability
that he or she agrees to respond, given that he or she is reached. And
neither of these two probabilities is ever known"
Link para o artigo:
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